A storage medium such as a Hard Disk Drive (HDD) and a memory are connected to a data processor such as a personal computer and a mobile phone. Some of the data processors permit certain users to read data stored in the storage device. Such data processor prevents data leakage, for example, by performing a user authentication, thereby prohibiting unauthorized users from reading data stored in the storage device. The storage device connected to the data processor may be removed from the data processor and may be connected to another data processor that does not perform a user authentication. In this case, data stored in the storage device may be read by the data processor that does not perform a user authentication and may be leaked to an unauthorized user. Moreover, even if data stored in the storage device is encrypted and a password is set, the password may be analyzed and thereby the data may be decrypted after the storage device is connected to another data processor.
Fujitsu Laboratories' “Fujitsu Develops Secure USB Memory Device Featuring Automatic Data-Erase Function” Apr. 17, 2009 press release discusses a storage device that performs a leakage prevention process such as erasing data stored on the storage device when the storage device is connected to a data processor that is different from a registered data processor. Japanese Laid-open Patent Publication No. 2007-323149 discusses a storage device that notifies the occurrence of unauthorized access to an external device when the unauthorized accesses to a storage device from an unregistered data processor reaches or exceeds a specified number of times.